Latent State - Viral Genetics

THE LATENT STATE

Temperate viruses can infect a cell and enter a latent state that is characterized by little or no virus production. The viral DNA genome is replicated and segregated along with the cellular DNA when the cell divides. There exist two possible states for the latent viral genome. It can exist extrachromosomally like a bacterial plasmid, or it can become integrated into the chromosome like the bacterial F factor in the formation of a high-frequency recombination (HFR) strain . Because the latent genome is usu-ally capable of reactivation and entry into the lytic cycle, it is called a provirus or, in the case of bacteriophages, a prophage. In many cases, viral latency goes undetected; how-ever, limited expression of proviral genes can occasionally endow the cell with a new set of properties. For instance, lysogeny can lead to the production of virulence-determining toxins in some bacteria (lysogenic conversion) and latency by an animal virus may pro-duce oncogenic transformation.